1. Field of the Invention
The present invention relates to a high pressure supply pump with a lifter guide for supplying fuel to an internal combustion engine (hereinafter called xe2x80x9cenginexe2x80x9d) and a method of manufacturing the lifter guide.
2. Description of Related Art
A high pressure fuel pump having a cylindrical tappet guide (lifter guide) for guiding a tappet (lifter) is known. The tappet guide disclosed in JP-A-10-141178 is formed separately from a housing and connected thereto. Since an area of an engine head in which the high pressure fuel pump is installed is limited and a larger outer diameter of the tappet is required, it is preferable that wall thickness of the tappet guide is as thin as possible. Axial length of the tappet guide is relatively long to accommodate a spring urging a plunger toward the tappet. Further, the tappet guide is provided at a circumferential wall thereof with an opening through which air, fuel or oil is sucked into or ejected out of an interior thereof when the tappet reciprocatingly moves along an interior wall of the tappet guide. In case of a cylindrical member, such as the tappet guide mentioned above, having thin wall thickness and relatively high dimensional and shape accuracy, it is common that rough shape of the cylindrical member is formed at first, typically, by drawing or cold forging and, then, final shape of the cylindrical member is formed, typically, by machining inner diameter thereof to secure demanded dimensional and shape accuracy.
However, on machining the tappet guide, the tappet guide is clamped to a process machine. The dimensional and shape accuracy of the tappet guide is generally assured in a state that the tappet guide is clamped to the process machine. Since clamping force applied to the tappet guide attached to the process machine during machining is not applied to the tappet guide detached from the process machine after machining, shape of the tappet guide attached to the process machine during machining is prone to differ from that detached from the process machine after machining, unless the circumferential wall of the tappet guide has adequate stiffness. To secure the adequate stiffness of the circumferential wall of the tappet guide, very thin wall thickness of the tappet guide can not be realized. Further, the opening of the tappet guide is formed by drilling so that, after having formed the opening, it is required to have a process of removing burrs at a circumferential periphery of the opening, which results in increasing manufacturing cost.
On the other hand, in case of a high pressure supply pump disclosed in JP-A-10-30525, a tappet guide is formed integrally with a housing. For machining the tappet guide, a portion of the housing except the tappet guide can be clamped to the process machine so that the clamping force is not directly applied to the tappet guide. Accordingly, shape of the tappet guide in a state that the housing is attached to the process machine does not differ from that in a state that the housing is detached from the process machine. This makes it possible to form the tappet guide having thinner wall thickness.
However, since the tappet guide formed integrally with the housing, typically, by forging is roughly shaped, a relatively large amount of the wall thickness of the tappet guide has to be removed by machining so as to form the tappet guide having thinner wall thickness with higher dimensional and shape accuracy, which results in more fabrication time and higher manufacturing cost. Further, the drilling process of forming the opening of the tappet guide becomes necessary so that more fabrication time is required.
An object of the present invention is to provide a compact high pressure supply pump having larger discharge amount and higher discharge pressure and incorporating a lifter guide whose wall thickness is thinner and which is easily formed with less fabrication time.
Another object of the present invention is to provide a method of manufacturing a lifter guide whose wall thickness is thinner and which is easily formed with less fabrication time.
To achieve the above object, in the high pressure supply pump in which a drive force of a drive cam is transmitted via a lifter to a plunger slidably and reciprocatingly movable in a cylinder of a housing, a lifter guide is positioned around a circumferential wall of the lifter and fixed to the housing concentrically with the plunger so as to guide the lifter to move reciprocatingly therein. A circumferential wall of the lifter guide has a seam bridging at least a part of a gap extending from an axial end to the other axial end thereto.
The lifter guide mentioned above can be easily manufactured, for example, by rounding a flat plate in cylindrical shape and seaming opposite circumferential ends. This means that thinner wall thickness of the lifter guide can be secured through a relatively simple fabrication process, compared to the conventional lifter guide formed by machining or forging and machining. The thinner wall thickness of the lifter guide causes the lifter to have larger outer diameter so that an area of the lifter in contact with a cam surface of the drive cam is larger. This makes it possible to have wider width of the cam surface of the drive cam and to have larger lift amount of the drive cam. Accordingly, discharge amount and discharge pressure of the high pressure supply pump are larger, compared to those of the conventional high pressure supply pump whose body size is equal to that of the high pressure supply pump. In other words, body size of the high pressure supply pump is more compact, compared to that of the conventional high pressure pump whose discharge amount and discharge pressure are equal to those of the high pressure supply pump.
It is preferable that the gap is not entirely seamed so that a part of the gap constitutes an opening. When the lifter moves recirocatingly in the lifter guide, air, fuel or oil in an interior of the lifter guide can flow through the opening from the interior to an exterior of the lifter guide or from the exterior to the interior thereof so that the air, fuel or oil does not affect as drive resistance against the lifter.
Further, it is preferable that the lifter guide unfolded circumferentially by cutting off the seam is provided at a circumferential end thereof with a projection and at another circumferential end thereof with a recess to be fitted to the projection. This construction serves to easily fabricate the lifter guide, since, when the flat plate is rounded cylindrically, the projection is easily fitted to the recess.
Preferably, a circumferential height of the projection is shorter than a circumferential depth of the recess so that an opening is formed between a top of the projection and a bottom of the recess when the projection is fitted to the recess. The opening, through which air, fuel or oil passes, can be easily formed.
Furthermore, it is preferable that the circumferential wall of the lifter guide has another opening circumferentially apart from the opening. In a case of a high speed and high revolution engine in which the lifter moves at high speed, the air, fuel or oil can be smoothly sucked and ejected not only through the opening but also through the another opening.
Moreover, preferably, thickness of the circumferential wall of the lifter guide is not thinner than 0.5 mm but not thicker than 2.0 mm. The conventional lifter guide formed by machining needs over 2.0 mm wall thickness to secure stiffness with which the lifter guide is not substantially deformed after being detached from a process machine. On the other hand, the lifter guide whose wall thickness is not thicker than 2.0 mm can be easily fabricated by rounding a flat plate in cylindrical form. However, the lifter guide whose wall thickness is thinner than 0.5 mm is short of strength demanded for the lifter guide itself.
Still further, it is preferable that the seam and the gap are positioned on a diametrical line of the lifter guide whose direction crosses a cam surface center line of the drive cam at a given angle thereto, preferably, perpendicularly thereto. Since the lifter is inclined in the interior in the lifter guide in a direction of a cam surface center line of the drive cam, the lifter never contacts the seam and the gap positioned on a diametrical line of the lifter guide whose direction crosses the cam surface center line of the drive cam.
A method of manufacturing the lifter guide is comprised of steps of forming a flat plate whose periphery line is provided with a projection and whose another periphery line circumferentially opposed to the periphery line is provided with a recess, then, rounding the flat plate circumferentially so as to cause the periphery line to abut on the another periphery line so that the flat plate is formed in generally cylindrical shape and the projection is fitted to the recess, and seaming al least partly the periphery line with the another periphery line to reinforce fitting between the projection and the recess.
According to the method mentioned above, thinner wall thickness of the lifter guide can be achieved with a simpler process, compared to that of the conventional lifter guide formed by forging or machining.
It is preferable to adjust inner diameter of the flat plate formed in cylindrical shape to predetermined shape and dimension when the flat plate is rounded, for example, by inserting a forming tool whose diameter is a given value into the flat plate formed in cylindrical shape and, then, pressing inward the flat plate formed in cylindrical shape from an exterior thereof. This process serves to secure higher shape accuracy of the inner diameter of the lifter guide.